A comprehensive biomechanical evaluation of length and diameter of dental implants using finite element analyses: A systematic review

Background With a wide range of dental implants currently used in clinical scenarios, evidence is limited on selecting the type of dental implant best suited to endure the biting force of missing teeth. Finite Element Analysis (FEA) is a reliable technology which has been applied in dental implantology to study the distribution of biomechanical stress within the bone and dental implants. Purpose This study aimed to perform a systematic review to evaluate the biomechanical properties of dental implants regarding their length and diameter using FEA. Material and methods A comprehensive search was performed in PubMed/MEDLINE, Scopus, Embase, and Web of Science for peer-reviewed studies published in English from October 2003 to October 2023. Data were organized based on the following topics: area, bone layers, type of bone, design of implant, implant material, diameter of implant, length of implant, stress units, type of loading, experimental validation, convergence analysis, boundary conditions, parts of Finite Element Model, stability factor, study variables, and main findings. The present study is registered in PROSPERO under number CRD42022382211. Results The query yielded 852 results, of which 40 studies met the inclusion criteria and were selected in this study. The diameter and length of the dental implants were found to significantly influence the stress distribution in cortical and cancellous bone, respectively. Implant diameter was identified as a key factor in minimizing peri-implant stress concentrations and avoiding crestal overloading. In terms of stress reduction, implant length becomes increasingly important as bone density decreases. Conclusions The diameter of dental implants is more important than implant length in reducing bone stress distribution and improving implant stability under both static and immediate loading conditions. Short implants with a larger diameter were found to generate lower stresses than longer implants with a smaller diameter. Other potential influential design factors including implant system, cantilever length, thread features, and abutment collar height should also be considered in future implant design as they may also have an impact on implant performance.


Introduction
Over the past decades, dental implants have become a reliable option for the treatment of missing teeth and the improvement of life quality, as evidenced by several clinical studies [1][2][3].However, in cases where there is alveolar crest atrophy with insufficient bone height and width, regular dental implants cannot be placed without additional bone augmentation [4,5].Multiple research efforts have been proposed to simplify the procedure and minimize complications under these situations [6].Consequently, narrow or short implants, which are usually defined as implants with a diameter between 3 and 3.5 mm or shorter than 10 mm, have been recommended as a solution for these challenging clinical situations, and their popularity in dental implantology is increasing [7,8].In many cases, the use of narrow or short implants can significantly reduce patient morbidity and allow for quicker definitive prosthetic rehabilitation.
Despite the advantages of narrow or short implants, their application is limited.These implants have smaller contact areas with the bone compared to standard implants, which may result in biomechanical instability and reduced mechanical strength, particularly in high occlusal load areas [9].Various clinical and experimental studies have examined the shortcomings by evaluating the key factors of implant success [10].Implant parameters including implant diameter and length are in the spotlight [11].Due to the decreased length of short implants and the reduced diameter of narrow implants, their clinical use in fixed restorations must be carefully reviewed.In addition, despite the success of implantation, marginal bone loss (MBL) may occur, which remains a major complication and a controversial issue in bone and oral health [12].
Although traditional methods, such as strain gauge and photoelastic stress analysis, have considerably advanced the evaluation of stress distribution, they display limitations.For example, strain gauges could only record the strains on a specific surface, which may have some limitations due to the geometry of the structure they bonded [13].Similarly, the results of photoelastic stress analysis are limited in the dental community due to their characteristics.FEA is a reliable approach for biomechanical evaluation in dental implant research to determine the distribution of stress affecting dental implants due to its multiple advantages over traditional methods.FEA to produce quantitative and qualitative biomechanical data in dentistry has received multiple attentions as they are effective in assessing stresses and load distribution on the restorations, implants, and peri-implant tissues under functional forces.It allows for the exploration of certain parameters, such as implant length and diameter, through iterative analysis with no ethical implications that would be difficult to achieve in clinical settings [14].Other advantages of FEA in dentistry encompass their ability to be applied for high-throughput analysis and the mimicking of complex structures showing irregular geometry [15].For example, the stress distribution at the bone and implant level in the case of MBL could also be studied with the help of FEA [12].With the help of FEA, clinicians may evaluate stress distribution in the contact area between the surrounding bone and dental implants, which could be a critical part of the success of implantation [16].
However, since FEA is an in-silico numerical analysis, certain limitations must be considered when evaluating its results before a clinical decision.The absence of pH simulation, temperature, biofilm, and the use of isotropic materials are examples of limitations that should be taken into account when evaluating FEA results [17].In addition, FEA requires detailed modeling and multifaceted scheming with correct boundary conditions [18].In addition to FEA, some other computational methods like machine learning and deep learning have also been applied in some recent research.For example, one study evaluated two automatic systems classifying the size of implants based on periapical radiographs with deep learning and clustering [19].Another study developed a machine learning model that can predict the failure of dental implants and peri-implantitis as a tool for maximizing the success of dental implants [20].
The appropriate choice of implant diameter and length would reduce stress distribution in cancellous bone, leading to a reduction in further bone resorption [21].Although extensive studies have been performed in this area, a conclusive conclusion has not been drawn, especially with a comprehensive consideration of both the length and diameter of dental implants.Accordingly, it is therefore important to elucidate the specific roles of the length and diameter of dental implants and the extent of their effects.The objective of this study was to sum up the current literature and to give a comprehensive consideration of both the diameter and length of dental implants concerning biomechanical properties using finite element analyses.The hypothesis of this study was that the implant diameter is more important than the implant length in the stress distribution of dental implants.

Materials and methods
This study was registered at PROSPERO under number CRD42022382211 and performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines [22].
The guiding question was formulated through the PICO format, with (P) presenting the participants, (I) indicating the intervention, (C) standing for the comparison, and (O) representing the outcome [23].Specifically, it was, "In scenarios with partially edentulous (P), what are the influences of dental implants (I) that are designed with various diameters and lengths (C) on the stress distribution during function evaluated by Finite Element Models (O)?"

Search strategy
An extensive search was performed in PubMed/MEDLINE, Embase, Web of Science, and Scopus for studies published from October 1993 to October 2023.The keywords used were: (finite element analysis) AND (dental implant) AND (diameter) AND (length).The specific search strategies used for each database have been provided in Table 1.Gray literature searches were also performed on the SciELO and Open Access Theses and Dissertations.To complement the study, a manual search of the reference lists from selected articles was supplemented with the database search.

Eligibility criteria
The following inclusion criteria were performed to identify publications: (1) peer-reviewed research publications written in English; (2) in vitro mathematical studies; and (3) studies that evaluated the biomechanical properties of both implant length and diameter using finite element analysis.
Studies were excluded based on the following criteria: (1) literature reviews, prospective studies, in-vivo studies, retrospective studies, and animal studies; (2) studies written in other languages; (3) research on orthodontic implants; and (4) studies that did not include dental implants with a diameter between 3 and 3.5 mm or shorter than 10 mm.

Study selection
After unifying relevant information and removing duplicate entries, the abstract and title of returned publications were assessed according to eligibility criteria by two reviewers independently.Articles assessed ineligible by both reviewers were immediately excluded, while articles considered ineligible by one reviewer but eligible by another were retained for full text reading.Two investigators working together read all full-text articles not excluded.Those eligible articles were retained to perform data extraction.Any disagreements were further resolved by discussion with all authors to reach an agreement.
Data from the included studies were gathered meticulously.A report of the following information was extracted: author(s), year of publication, area, bone layers, type of bone, design of implant, implant material, diameter of implant, length of implant, stress units, type of loading, experimental validation, convergence analysis, boundary conditions, parts of Finite Element Model, stability factor, study variables, and main findings.

Quality assessment
The quality assessment was performed in accordance with a previous research [24].The included studies were scored in accordance with six predefined criteria, including design of the implant model, design of the prosthetic restoration, bone model, type of loading, number of elements, and model dimensions (Table 2).

Study selection
A total of 852 references were retrieved from the database (158 from PubMed/MEDLINE, 143 from Embase, 179 from Scopus, and 372 from Web of Science.After removing duplicates, 431 studies were left, and 361 of these were excluded after evaluating their titles and abstracts.30 studies were further excluded upon full-text reading for not meeting the eligibility criteria.None of the 66 studies obtained from the gray literature was considered eligible.Eventually, 40 studies were included in this systematic review (Fig. 1).

Characteristics of the studies
A summary of the data extracted from the selected researches is displayed in Table 3.In terms of the area of dental implants, both maxilla and mandible models were evaluated in selected studies, and most studies evaluated the stress distribution of dental implants in the posterior region.Regarding the bone models, all applied cortical-layered and trabecular-layered bone models.Implant diameter and length also varied in selected researches due to their different focus and objectives.Type II bone was the most widely used bone type in the literature, and other kinds of bone were also programmed.The implant design varied among the studies such as threaded, cylindrical, screwed, or tapered implants, with most using pure titanium implants.For the measurement of the stress distribution, von Mises MPa was applied in dominant studies, while other studies with tangential stress were recorded in MPa or strain in μStrain.As for the loading conditions, static loading was applied in most studies since only 5 studies utilized immediate loading in the FEA models.Axial load was applied in 17 studies, while the other 23 studies reported loading in multiple directions.Among the 40 studies included, only one study conducted experimental validation for FEM and 11 researches used convergence analysis.Boundary condition was applied in most included studies by constraining the displacement of the nodes in all directions.
Table 4 summarizes the main findings of the 40 studies.Most studies utilized three components of the FEA model, which are trabecular bone, cortical bone, and implant.Abutment and superstructure were also considered in certain studies.Regarding the stability factor, the models were generally fixed at the bottom and sides of the bone to ensure zero movement in the degree of freedom, and all the components and the bone were usually assumed to be perfectly bonded.The literature also suggests other factors that may influence peri-implant stress, such as bone characteristics, implant system, cantilever length, thread features, and abutment collar height.Implant diameter and length mainly influence the stress distribution in cortical and cancellous bone, respectively.The diameter of dental implants is more important than implant length in reducing bone stress distribution and improving implant stability under the FEA model.The diameter of dental implants is considered to have an impact in minimizing peri-implant stress concentrations to avoid crestal overloading.In terms of stress reduction, the length of dental implant gains increasing relevance with reducing bone density.Short implants with a larger diameter were found to generate lower stresses than longer implants with a smaller diameter.Due to the results of different implant lengths and diameters in FEA models, no numerical answer could be concluded in terms of what periimplant stress distribution increases, and it remains unclear what interaction between the diameter and length of dental implants exists.

Quality assessment
A total of 40 studies were evaluated and ranked based on the information presented in Table 5.In general, most of the studies utilized complex or very complex bone models.However, when it comes to the design of the implant, only 23 of the selected studies employed commercially available implant designs, which limited the scope of the research.While 23 studies reported loading in multiple directions, the remaining 17 studies only applied axial load.The majority of studies featured more than 100,000 elements, with only 2 studies using two-dimensional FEA.As for prosthetic restoration, 16 studies utilized crowns or bridges as a superstructure to enhance the FEA model's reliability.Due to the unavailability of meta-analysis data such as means, standard deviations, and sample size in FEA studies, a systematic synthesis approach was adopted based on the research questions proposed to thematically explore the results and methods.

Discussion
This study aimed to assess the impact of both the diameter and length of dental implants on biomechanical properties using FEA.The included studies have reached a noteworthy conclusion that both implant diameter and length have a significant influence on the stress distribution of both cortical and cancellous bone under both static and immediate loading on dental implants or prosthetics.The findings of this study suggest that the diameter of dental implants is more important than the implant length in reducing bone stress distribution and improving implant stability under both static and immediate loading conditions, which is in accordance with the hypothesis of this study.
Implant diameter is one of the most critical parameters in dental implant design, as it significantly impacts the stress distribution around the implant-bone interface, particularly in cortical bone.Studies have indicated that implant diameter primarily affects the cortical peri-implant regions, with stress peaks of the cortical bone decreasing as the implant diameter increases [27].In addition, when placing wider dental implants in the bone, a significant reduction of tensile and compressive stress values was observed.Eazhil et al. reported a significant reduction in von Mises stress with an increase in implant diameter [37].Furthermore, increasing implant diameter can resolve the high-stress concentration caused by increasing cantilever length [28].However, it should be noted that in low-density bone, the use of narrow-diameter implants with a taper in the crestal region must be avoided to ensure safety.
The length of a dental implant is the most influential factor in determining the magnitude of Max von Mises stress in the implantabutment connection, with longer implants promoting more even stress distribution in trabecular bone compared to shorter implants.According to studies, implant length is a more crucial parameter than diameter in reducing cancellous bone stress under both axial and buccolingual loads [51].With the increase in implant length, a decreased tendency towards peri-implant stress may occur, resulting in more effective and homogeneous stress distributions in trabecular bone [64].When short implants are used, stresses in cancellous bone and strains in cortical bone increase significantly compared to standard implants [31].The values of strains obtained from short implants were significantly higher compared to long implants, which exceeded the limitations of strains in the cancellous bone.However, Demenko et al. proposed that short implants with an appropriate length and diameter could avoid overstress in surrounding bone, even in low-quality bone [30].In some cases where there is insufficient bone quantity, an implant length of 6 mm can be used if the bone width is sufficient [51].
A previous meta-analysis compared the survival rate of standard-diameter implants and narrow-diameter implants and indicated guidelines and recommendations for the application of narrow-diameter implants [7].Another systematic review evaluated short implants concerning biomechanical properties and detected the most relevant parameters using FEA [24].Accordingly, the main goal of the present review was to conduct a comprehensive assessment of the influence of both the diameter and length of dental implants.While the implant length presents an impact on stress distribution, the diameter is considered the most significant variable affecting stress distribution in the implant, abutment, and bone [37].Some researchers have suggested that both diameter and length play an equal role in stress reduction [40].However, most of the included studies suggest that diameter has a greater effect than length in reducing cortical bone stress and increasing implant stability under both static and immediate load [32,35,47,51].For single crown restoration, Kheiralla et al. found that short implants were better than narrow-diameter implants, and another study found that short implants with a large diameter had lower stresses than long implants with a small diameter, supporting Kheiralla et al.'s conclusion [28,46].After inserting 12 different implant diameters and lengths based on a CBCT model of the mandible, Shinya et al. concluded  The models were fixed at the bottom and sides of the bone so that they had zero movement in the degree of freedom (DOF).

Implant diameter, implant length, type of implant
The triple cylindrical implants, with a new implant design, showed appropriate results in terms of abutment, implant, and bone tissue stress.Borie et al. [30] 2016 Implants, abutments and frameworks All abutments were fixed to the implant based on a perfect adaptation and a complete joint.
The implant was considered to be completely osseointegrated.

Implant lengths, connections, locations, and restoration materials
The implant connection system, length, restoration material, and type of prosthesis influence the stresses at the peri-implant bone.Implants of 10 mm in length exhibited higher stress values.buccolingual loading as compared with vertical loading, but diameter had a more significant effect than length to relieve the crestal stress and strain concentration.Ding et al. [36] 2009 Cancellous bone, cortical bone, implant, It was modeled using nonlinear frictional contact elements, which allowed minor displacements between implant and bone.

Diameter of implant
With an increase of implant diameter, stress and strain on the implant-bone interfaces significantly decreased, especially when the diameter increased from 3.3 to 4.1 mm.Eazhil et al. [37] 2016 Cancellous bone, cortical bone, implant, Implants were estimated to be completely osseointegrated.
Implant diameter, length There was statistically significant decrease in von Mises stress as the implant diameter increased.Elleuch et al. [38] 2021

Jaw bones, implant and abutment
The interfaces between the native teeth, the cortical and cancellous bones are treated as perfect bonding.
Diameter, length and thread's pitch The implant diameter is identified to be the dominant variable.The maximum equivalent stresses in the abutment, implant, and jaw bones decrease considerably with the increase of the implant diameter.Faegh et al. [39] 2010 Trabecular bone, cortical bone, implant All the components and the bone were assumed to be perfectly bonded.

General contour, external threads
The slope and length of the implant collar, and the implant diameter influence the interfacial stress levels the most, and the effects of changing these parameters are significantly noticed only in the cortical bone area.Forna et al. [40] 2020 Implant, abutment, bone The contact type between bone and implant was defined to be perfectly bonded.

Implant diameter, length and type of bone
Diameter and length play an equally important role in decreasing stress.

Georgiopoulos et al. [41] 2007
Cortical bone, Trabecular bone, Dental implant & abutment, Superstructure The contact surfaces of implant and surrounding bone were always bonded, with no sliding permitted (fixed bond).

Implant diameter, length
The FEA results indicated a tendency towards stress reduction on the implant when the length was increased.As far as bone tissue was concerned, there was a tendency towards strain reduction when the length of the implant was increased from 10 mm up to 14 mm.Guan et al. [42] 2010 Cancellous bone, cortical bone, implant, Fifty Percent Osseointegration Between Implant and Bone The interface surrounding an implant includes both blood and bone fragments.
Implant diameter, length, Young's modulus of cancellous bone, Young's modulus of cortical bone, the cortical bone thickness The implant length is more influential within cancellous bone than the diameter.However, implant diameter is more influential in cortical bone.Gümrükçü et al. [43] 2018

Cancellous bone and cortical bone
We assumed that there was excellent osseointegration in boneimplant interface in all models.
Implant number, length and tilting degree The ideal implant length is 11.5 mm.

Güzelce et al. [44] 2023
Cancellous bone, cortical bone, implant, Abutment Screw Crown Temporary cement The denture and implant were provided with bonded contact for all models.
Implant diameter, framework materials Mini-implants produce signifcantly higher stress values in the supporting tissues and implant neck than standard implants.Himmlová et al. [45] 2004

Bone and implant
The interface between the implant and the bone was modeled as an immovable junction.
Implant diameter, length An increase in the implant diameter decreased the maximum von Mises equivalent stress around the implant neck more than an increase in the implant length, as a result of a more favorable distribution of the simulated masticatory forces applied in this study.Kheiralla et al. [46] 2014 Trabecular bone, cortical bone, implant All components were constructed in a way that ensures 100% contact along interfaces with no gaps or interferences.

Size of implant, loading conditions
Standard and short-wide implants could be a better choice than narrow implants in supporting single-unit restorations.Kong et al. [47] 2008

Cortical bone, Cancellous bone
The implant was rigidly anchored in the bone model along its entire interface.
Implant diameter, length Implant diameter and length favor stress distribution in cortical bone and cancellous bone, respectively.Implant diameter exceeding 3.9 (continued on next page) P. Qiu et al.  [48] 2009 Cancellous bone, cortical bone, implant, The prosthesis-abutment interface was considered to be bonded.
Implant diameter, length Exceeding 4.0 mm and longer 11.0 mm are the best combination for optimal biomechanical properties in immediate loading implants in the type B/2 bone.Kong et al. [49] 2009 Cancellous bone, cortical bone, and implantabutment For simulation, a ''fixed bond" condition was set to its interface with the bone.

Implant diameter, length
The implant diameter affected stress distribution in jaw bone more than length did; and an implant diameter exceeding 3.9 mm and implant length exceeding 9.5 mm was the optimal selection for type B/2 bone in a cylinder implant by biomechanical considerations.Li et al. [50] 2009 Cortical and cancellous bones, implant-abutment complex A bond condition was set at its interface with the bone.

Implant diameter, length
In type IV bone, implant length is more crucial in reducing bone stress and enhancing the stability of implant-abutment complex than implant diameter.Biomechanically, implant diameter exceeding 4.0 mm and implant length exceeding 9.0 mm are the combination with optimal properties for a screwed implant in type IV bone.Li et al. [51] 2011 Cancellous bone, cortical bone, implant During the simulation, a bond condition was set at its interface with the mandibular bone.that stress distribution on surrounding bone was found to reduce with increasing length but mainly in implant diameter [62].Therefore, to minimize the risk of overloading and improve implant stability, the diameter of the dental implant should be considered a more important parameter than implant length during the design process.
The longevity of implants relies on both endogenous and exogenous factors.Apart from exogenous factors such as the diameter and length of implants, endogenous factors including bone quality and quantity are also essential for the success of implantation.Type IV bone is defined as a thin layer of cortical bone surrounding trabecular bone with poor strength and low density [50].This bone quality is typically found in the posterior maxilla, which is the primary area for tooth loss and the main region for masticatory activity.Accordingly, it is critical to investigate the role of implant diameter and length in these regions.However, few studies in this review examined the impact of implants with various lengths and diameters on poor-quality bone.One such study concluded that a screwed implant with a length of 12 mm and a diameter of 4 mm is the optimal combination for the posterior region of lower teeth with low density [51].In addition, Li et al. concluded that dental implants with a diameter of 4 mm and a length of 9 mm were the best choice for a screwed implant in Type IV bone [50].Therefore, evaluating the stability of short and narrow-diameter implants is essential under the conditions of placing these implants in Type IV bones.
The success of dental implantation depends on various factors, including implant diameter, implant length, bone quality, and other design factors such as thread features, implant system, and abutment collar height.Improving bone quality reduces bone strain values, and implants with 10 to 20-degree neck configurations are recommended to reduce strain values and enhance load dissipation in bone tissue [37,65,66].The implant connection system, type of prosthesis, and restoration material can influence stresses in peri-implant bone, and the thread features, length, and slope of the implant collar are other factors to consider.Distal cantilevers may cause high strain on the cervical cortical bone, which can be addressed by increasing implant diameter [28,32].Short implants exhibit the highest stress concentrations around the first threads for the screw, whereas long implants exhibit the highest von Mises stress at their neck [67,68].Small dental implants have stress concentrations at the threads in the cervical and middle regions, and trapezoid-shaped threads are preferable over saw-tooth threads for inducing compressive and tensile states at the cortical bone.Conical connection and switching platform with a dental implant system present lower maximum strains around peri-implant areas, and longer abutment collars concentrate stresses at both cortical bone and implant levels through enhancing crown-to-implant ratios [69,70].In summary, these potential influential design factors should be considered during clinical practice in implantology.
The loading condition is an essential part of the FEA, applying loadings from multiple directions can achieve a more reliable result.However, nearly half of the included studies only applied axial load, which may lead to limitations in the results.Accordingly, loading in multiple directions should be utilized in further studies to improve the reliability of the results of FEA.Boundary condition was also important in the FEA model.This condition was applied in most included studies as the models were generally fixed by restricting all degrees of freedom from the nodal point and preventing movement in all three axes.In addition, some researches also added a realistic The space in the mandibular ridge following virtual extraction was set to be automatically replaced by bone, so there was no bone in the space when the implant was placed.

Implant diameter, length
The stress on the peri-implant bone was found to decrease with increasing length and mainly in diameter of the implant.
Ueda et al. [63] 2016 Trabecular bone, cortical bone, implant, NA Thickness of the cortical bone, Young's modulus of the trabecular bone, and the diameter and length of the implant Implants of proper length or diameter could limit the maximum equivalent strain in peri-implant bone except when both the thickness of the cortical bone and the Young's modulus of the trabecular bone are small.Vairo et al. [64] 2013 Cancellous bone, cortical bone, implant Complete osseous integration between implant and bone tissue was assumed.
Implant design, in-bone positioning depth, and bone posthealing crestal morphology The implant diameter can be retained as a more effective design parameter than the implant length.A significant reduction of stress peaks, mainly at the cortical bone, occurred when implant diameter increased.Nevertheless, implant length exhibited a certain influence on the bone-implant mechanical interaction at the cancellous interface, resulting in more effective and homogeneous stress distributions in trabecular bone when the implant length increased.
NA: no applicable.
P. Qiu et al. approach to obtain the morphed geometry of the mandible and made the boundary condition more perceptible.Another important issue that needs to be considered is that only one study of this review conducted experimental validation for the FEA model and 11 researches used convergence analysis.Therefore, it is necessary to conduct experimental validation to confirm the results of the biomechanical evaluation of the length and diameter of dental implants with FEA.This study has several limitations.Firstly, it is important to note that FEA models are simulations, and the accuracy of FEA models depends on the input data and assumptions made during the process of modeling.Therefore, results obtained from FEA models should be interpreted with caution and confirmed by in vivo and in vitro studies.Moreover, the present study only considered the effects of the length and diameter of dental implants on peri-implant stress distribution, while other factors, such as occlusal forces and implant placement techniques, were not considered.Future studies should take these factors into account for a more comprehensive understanding of implant biomechanics.

Conclusions
Based on the findings of this study, the following conclusions were drawn.
1. Implant diameter and length mainly influence the stress distribution in cortical and cancellous bone, respectively.2. Implant diameter demonstrated a more significant effect compared to implant length in reducing bone stress distribution and enhancing implant stability.3. Short implants with large diameters presented lower stresses than the long ones with small diameters.4. Implant system, cantilever length, thread features, and abutment collar height should also be considered.

Table 5
Total scores of included studies.

Fig. 1 .
Fig. 1.Flow chart of the literature research and results.

Table 1
Electronic databases used and search strategies.

Table 2
Criteria for quality assessment.

Table 3
Summary characteristics of the included studies.
μStrain(continued on next page) P.Qiu et al.

Table 3
(continued ) (continued on next page) P.Qiu et al.

Table 3
(continued ) (continued on next page) P.Qiu et al.

Table 4
Summary of findings of included study.